In many industrial processes and in fluid production systems, a slurry of solids suspended in a liquid is produced and it becomes necessary to separate the solids from the liquids so that each material may be treated in ways that will make disposal or use of the treated materials both economical and environmentally effective. In most such processes or systems, the slurry material is fed to a filter apparatus which may take many forms including a belt press, a vacuum filter or a pressure filter. In one form of pressure filtration system a pair of plate members form an internal space chamber separated by a filter media of some form. The plate members are pressed together at mating surfaces with the filter media positioned between the mating surfaces and spread across the interior space separating one plate from the other plate. Slurry materials are fed into one plate and into the chamber while filtrate liquids are taken away from the other plate leaving behind the solids of the slurry accumulated on the filter media. After a sufficient amount of slurry has been treated to accumulate solid materials, the plates are separated and the filter media is replaced and the filtration process is repeated with a clean filter media. The filtrate fluid and solids are then separately used, treated or disposed of in an acceptable manner.
The prior art apparatus of the nature of the above described apparatus have used pressurized gas or vacuum filtration to extract the fluids from the slurry materials. Vacuum-atmosphere pressure differentials have not been effective in creating "dry" solids in the filter cakes they produce and only marginally produce solids in filtrate. Other technologies used in filter apparatus have employed elastomeric diaphragms within the chamber with the diaphragm hydraulically (or pneumatically) actuated to create pressure differentials to squeeze out liquids from solids. Such systems may use compressed air (sometimes called "air-fluff") following the hydraulic diaphragm squeeze to drive out interstitial liquid. Such systems are not as cost effective as pressurized gas filtration because those systems usually require both the air pressure step as well as the diaphragm squeeze to produce dry solids. Further, elastomer diaphragms limit the chamber size and hence limit the solids cake size that can be produced and thus the filter effectiveness. In addition, heat and chemicals may adversely effect elastomer diaphragms. Also, the diaphragm and air squeeze systems add time to the filtration cycles resulting in lower efficiency and lower production rates.
In a prior U.S. Pat. No. 5,059,318, issued Oct. 22, 1991 to the present inventor, there is disclosed a system and apparatus for producing an effective seal between mating filter plates in a manner to substantially reduce or completely eliminate leakage of slurry fluids between the mating filter plates. The present invention relates to such a filter apparatus and discloses the apparatus and method for producing an effective separation of liquids and solids in a slurry material. In the filtration process of the present apparatus and method air, gas and liquid cycles are used in the filtration process to produce an initial high pressure squeeze to clear liquid from solids in the slurry and to drive free interstitial liquid from the solids cake.